How long would it take for two human populations to become a distinct species?

Factual Questions
21

No, this is blatantly incorrect. Normally two populations are geographically separate (allopatric) during the time of “species emergence,” and do not interbreed at all. Depending on what kind of genetic differences have developed while they were isolated, when the populations come back into contact they may either still be able to interbreed, and thus merge again as a single species; or be incapable of interbreeding, and thus be separate species. Often, however, the two populations may be able to hybridize, but hybrids are at a selective disadvantage compared to pure individuals of each type. Individuals that mate only with their own kind will be selected for, accelerating the process of species formation. But this is not a matter of “members of a species that can mate and produce offspring with both the old species and the new one”; many members of both populations will be able to hybridize.

There is no such thing as a “protomutation stage.”

Absolutely wrong.

Complete nonsense. As I said, there is no such thing as a “proto” stage.

You here seem to be talking about a process of sympatric speciation, in which speciation occurs within a single geographic population. By far the most common mechanism of speciation seems to be allopatric speciation; it has been fiercely debated whether sympatric speciation is even possible. Some research has documented a few cases; but even in these cases the populations are separate on a micro scale, as in different food plants or different levels of the same lake. Even so, it’s not a case of “one or the other species will emerge.”

Sorry, this makes no sense at all. Hybrids between two species are not genetically members of either species; they are hybrids.

Mitochondrial Eve existed at approximately the same time as the emergence of anatomically modern humans; estimates from genetics or fossils are not precise enough to determine that she pre-dated this event.

22

Not necessarily. If the populations are still interbreeding, then they’re likely not isolated enough to become separate species.

What is a protomutation stage?

No. You are confusing what happens in the real world with our human need to put clear boundaries around categories of things. Speciation is a process, not an event. Often, what we call species, are distinct populations that generally don’t interbreed, but which can do so if encouraged enough. Don’t focus so much on whether they can interbreed, but on whether they do interbreed.

No. M-Eve was a member of the species H. sapiens.

23

I misused the term Hybrid. My bad. I’m not using Genetic Lingo.

Genetically speaking a Hybrid is a mix of two species. I was using it as a member of one species capable of breeding with one of another.

You argue with me that there is no period of Genetic Emergence (where two genetic species are still interbreedable but eventually one emerges in a given population) but you’re the same person who says Genetic Drift explains evolution?

I think my muddled terminology has muddled your brain. Again, probably my bad.

For what it matters. M.Eve was possibly not modern Homo Sapiens Sapiens. It’s probable she was. I’ll stand by the possibility that she was a protomutation human( I know I made the term up ) - breedable with the race that would become humans. But she was not necessarily genetically a modern human.

Mitochondria and DNA are not the same thing. Mules have Horse Mitochondria, despite being a separate species. In my convoluted terminology a Horse would equal a protomutation Mule. Sloppy science, I’m sure, but if people really wanted the science, they’d go to a textbook on evolution.

Of course speciation is a process that takes generations. But its a process that starts with an event of mutation. The new species that emerges will probably not be the single event mutation species but a hybrid(used correctly) of that species and the original.

Whether or not we agree on how the theory of evolution works: I think we all agree that the larger the isolated population, the longer evolution is going to take.

The idea of Genetic Drift makes it possible that none of us are the same species of Humans that existed 200,000 years ago. It’s not like we have DNA that old to really test against. We’re just doing math and extrapolation based on what we know of the Human Genome and comparing bones. We certainly don’t look the same.

24

No, they come here for facts, not “sloppy science”. Beyond that, I’ll let Colibri, in moderator mode, advise of the rules of this forum.

No it won’t. A species emerging in isolation (the most common form, as **Colibri **noted) will not have any hybrids. You seem to think that a new species emerges as an individual in a population who could not breed back with that population. Wrong. Think of it like a ring species, where populations A and C can both breed with population B, but A and C cannot breed with each other.

Probably, but not necessarily. It also depends on how rapidly the environment is changing.

We certainly do. Why do you think that population is often referred to as Anatomically Modern Humans?

25

Nobody here uses science properly. We all interpret, trying to communicate with people who don’t use science at all. Sloppy Science is a necessity to communicate the basic ideas (though not the detailed facts) with laymen. If they want to speak expert, they don’t come to a general discussion forum

duh, read what I wrote and you’ll see we are saying the same thing.

Anatomically is not appearance unless you’re looking at a shadow play.
We’re taller, arguably smarter and occassionally have blue eyes and blonde hair, not to mention yellow or pink skin. We have more variation of feature shapes, eyes ears noses, etc.

Put a dozen new yorkers in a room with a dozen homo sapien sapiens from 200k years ago in the same room and it would take an anthropologist or geneticist to think they were of the same species. (They would be( by definition of the scenerio), but obvious to you and me - not so much)

On the brighter side of all this debate - at least no one has tried to bring up intelligent design.

26

Here’s an example.

Wolves, Canis lupis, and Coyotes, Canis latrans, are different species. But they can mate, and the offspring of matings between wolves and coyotes are fully fertile. So how can we call the coyote a separate species, according to the reproductive species model? Well, although wolves and coyotes CAN interbreed, it turns out that they hardly ever do interbreed. So here we have an example of prezygotic reproductive isolation. Wolves and coyotes are reproductively isolated and therefore separate species, not because they can’t interbreed, but because they don’t (usually) interbreed.

These articles in wikipedia might be helpful:

27

Many of us who post here are scientist. I am one, and so is Colibri. My background is no in biology; Colibri’s is. Many of us use science properly.

Utter bullshit.

No. What you are saying is factually incorrect. That is why some of us are correcting those errors.

“We” are all over the map in terms of height. The human population is not “Europeans”. Just because we have more variation (likely true, although we can’t say for sure), there is no reason to believe that those populations from ~200k years ago would not fit comfortably in the range of modern phenotypes.

I can’t figure out what this is supposed to mean.

This is not a forum where we try to have debates, unless we are forced to by people posting factually incorrect information.

28

That is most certainly untrue. A number of posters here are proper working scientists in their fields, and a greater number are informed amateurs. The fact you can’t be arsed doesn’t excuse presenting false information, to whit your bald statement one does not have archaic DNA. That is false, in fact DNA has been extracted from ancient bones, including Neanderthal.

Promoting ignorance by half assed answers is for other boards.

That is utterly incorrect. Simplification is one thing, making up things whole cloth and getting basic facts wrong is another (and this forum tries to be rather better than “make stuff up and pretend I know something”),

You most certainly were not.
You’re a newcomer here. Without engaging in junior modding, I’d suggest paying attention to the style and approach before waltzing in and making grossly incorrect statements.

29

Why do you think this? We aren’t taller. We don’t have larger brains. We don’t know for sure what skin color most people 200,000 years ago had. It’s certainly possible that they had more variability that modern humans, and that genetic diversity was greater 200,000 years ago than today. Heck, it’s even likely, since we think there was probably a bottleneck event 75,000 years ago. And that means that a lot of alleles were probably lost at that time.

No, it wouldn’t take a geneticist. It would be obvious that anatomically modern humans were human beings, that’s why we call them anatomically modern humans. It might be true that they would appear to belong to an ethnic group, or groups that don’t exist today–they might have unusual skin colors, or facial features, or hair colors and textures. But if you can recognize an Yanomamo, an Australian aborigine, a New Guinea highlander, an Ainu, a Tamil, a !Kung, a Zulu, a Swede, and a Spaniard as all belonging to the same species, you should have no trouble putting the 200,000 year old H. sapiens sapiens in the same species.

If you’re talking about Homo neanderthalensis, then you might be right. Neandertals probably looked different enough to be startling. Although perhaps not. But my suspicion is that Neandertals and H. sapiens sapiens had some sort of distinctive markers that would make them look different to each other. We commonly see that closely related species of monkeys tend to have different hairstyles–mustaches, beards, tufts, and such, and different skin colors or fur colors and patterns. And these are probably the result of sexual selection, and serve as ways for related species to identify members of their own species.

So it might be that while Neandertals and modern humans could interbreed, there would be some superficial differences about them that would make them appear unattractive or weird to our eyes.

30

Technically the OP wasn’t a factual question.

None of what was said here was factually inaccurate. The fact is that there are varying theories of how it actually works. What we know is what we can test in a lab. We can introduce mutation and test how it propogates in a population.

90% of Colibri’s posts have been about Allele propogration more than evolutionary propogation. I’m not convinced the theories he buys into are right, I’m not convinced he’s wrong either.

The facts are simple:

1)Isolate a population and some Alleles will propogate and some will disappear.

2)Mutation causes a genetic change.

The debate is over the interaction of those facts. I am unaware of any experiment that shows that new species can develop without mutation. I could be convinced that mutation may occur simultanously with certain combined Alleles, but I’d have to see the report.

The confusion really stems from what defines a new species. Genetic Drift alone doesn’t seem to cut it for me. It just explains propgration of Alleles (genetic traits). But variation in Alleles can go a long way and still remain the same species - same subspecies even. It’s less obvious in humans than in say, dogs.

Let’s face it, a new species is a hard goal to reach. Statistically, the odds are against it happening without some kind of population reduction - possibly due to a rapid change in environment (though Homo Sapiens Sapiens has seen several glaciation cycles, some of them rapid.) Basically, you’d need to reduce the population so that the traits defining the new species could propogate faster than the traits defining the old species or at some point you need to have the new species totally isolated until it is a contender to supplant the existant species.

If you split the human race into two equal groups and put one on a terraformed mars and leave one on earth, in a million years, you might have a new species on one of the two, but with populations that large, the differences will probably be just as superficial as the differences between us and the homo sapiens sapiens of 200k years ago.

Now if a comet crashes into mars and drops the population to a couple hundred, the odds are better of diverse speciation.

31

You realize its not even a globally accepted idea that we’re all human.

Scientifically it is, but not everyone sees science as the font of truth.

Science, up until the 19th Century, wasn’t sure.

Anthropological evidence definitely shows that people have been getting taller. While the H.S.S of yore do fit within “normal” for today they would be by no means average.

Its not certain the hair color, eye color, skin color of H.S.S. Yore, but there is a consensus that they were most likely dark skined, dark eyed and dark haired.

32

You’re confused about the secular trend for increased height. Sure, people have been getting taller over the last 100 years. But that doesn’t mean that we’re taller than we were 200,000 years ago. We’re taller than our recent ancestors–those who lived through the early industrial age and before that the agricultural age. But go back even earlier and you find that early hunter-gatherers were taller and healthier than their farmer descendants. We’re only now in the modern age getting a diet and lifestyle as healthy as our very early hunter-gatherer ancestors.

And even so, we’re talking about variations in average height. Even if early humans were much shorter on average (which they weren’t), a 5’ 6" person wouldn’t be so short as to seem freakish.

And while it is certainly true that if we had to guess what people 200,000 years ago looked like, darkish skin, brown eyes and brown/black hair would be the most likely choice, the fact is we just don’t know. Neither do we know if people then had straight or wavy or kinky hair, or something way out in left field.

So probably humans 200,000 years ago wouldn’t be similar to any extant ethnic group. But that doesn’t mean they’d stand out like a sore thumb if you put them in a room with a random sample of New Yorkers. There probably aren’t any Khoi-San in New York, and very few people with the same traits of yellowish skin, peppercorn hair, epicanthic folds, and steatopygia. But just because there aren’t any New Yorkers who are from that ethnic group doesn’t mean that people would do a double-take if they saw one walking down the street.

More wikipedia articles that might be helpful:

33

It most certainly is, and Mace and Colibimbri, among others, have given factual responses. It is not a question susceptible to an exact answer, but a factual response can certainly be given.

Rubbish. Your posts are riddled with misstatements, as well as obfuscating “pulling it out of my ass” terminology.

Please, stop hand waving and blowing smoke.

  • same subspecies even. It’s less obvious in humans than in say, dogs.

Speciation is not a “goal” it is something that happens…

If you want to engage in poorly informed speculation and rambling IMHO or Great Debates are the proper forum. This forum is for direct factual responses.

34

Evolution is, simply put, the change in allele frequencies in a population over time.

You appear to think that “alleles” and “mutations” operate separately; they do not. A mutation results in a new allele. The frequency of that new allele in the population, several generations hence, will depend on several factors, including but not limited to the population size and the relative fitness value of that allele. If the new allele is more or less selectively neutral, then its relative frequency will largely be determined by genetic drift - that is, it’s frequency will be largely randomly determined. It could reach fixation, or it could be eliminated entirely, or it could remain at variable frequencies depending on the particular generation.

Genetic drift is going to take much longer than natural selection, to be sure. The OP specified identical environments. This means that existing traits will vary more or less randomly, while new traits will possibly be subject to natural selection. Without knowing what these new traits are, it’s pretty much impossible to tell which will have greater influence on its subsequent frequency in the population in question.

The OP has already specified reduced populations of 1000 individuals each…

35

Re-reading the OP, I think there is a little more to it than we’ve been discussing.

If the two populations were to lose communication, and it looked to an outside, objective observer that it would be a permanent loss, then that observer could declare the two populations to be separate species then and there. They are two defined populations that do not interbreed and who are separated by geographical barrier (in this case, more properly called an outer spacial barrier) . If they were to be suddenly re-united, then they would be considered the same species if they commonly and successfully interbred and produced fertile offspring. That’s the Biological Species Concept, which is generally what is used for mammals.

Now, one might argue that humans aren’t really well covered by the Biological Species Concept since we don’t exist “in the wild” in the same sense as other non-domesticated animals. But that’s the best we have right now, so that’s what I’m going with.

36

That’s a true statement. But -
Allele frequency change != speciation.

I concede on the grounds of semantics.

I concede on the grounds that I’m a dumbass.

37

On the other hand, it is unlikely that any taxonomist would declare the Zig population to be a separate species from the Zog population (assuming both were known), regardless of interbreeding, as morphologically, they would likely be identical (at least initially). If anything, the best consensus you might get is that Zigs and Zogs constitute discrete populations of Homo sapiens. Phylogenetically, the two would almost certainly be indistinguishable (especially if the individuals for each population were selected at random from the entirety of the human population of Earth), as well as being indistinguishable from the population at large, so they would again be classified as a single species.

Which, of course, points out the additional problem that a species as a taxonomic entity may or may not conform to a species as a biological / evolutionary entity.

38

Oh, I’m sure that there would be plenty of rivers, mountain ranges, etc. between them.

39

:smack: I forgot the part about there needing to be a morphological difference between the populations. With a founding population of 1000 randomly chosen individuals, it shouldn’t take too many generations for that to appear. Throw in the high probability of those populations fracturing along racial/ethnic lines, and you accelerate that process. Throw in the possibility of that fracturing turning into warfare, and things change even faster.

40

[Moderator Note]

I’m going to step out of the discussion for a moment to make some comments on this. pan1, you’re new here and are evidently not familiar with the purpose and conventions of this board. Here at the Straight Dope, especially in General Questions, we do strive for factual accuracy. We make an effort to “use science properly;” “sloppy science” is not really necessary to communicate the basic ideas.

From the General Questions Rules at the head of this forum:

As has been mentioned previously, we do have experts who post here on many topics. I am a professional biologist of 35 years experience; a number of the other posters in this thread are very knowledgeable about speciation, genetics, and evolution. It is evident from your posts that you have only a rudimentary knowledge of these subjects; many of your posts here consist of misinformation, misinterpretation, errors, and speculation without a factual basis. We would like to discourage such postings here; they are not helpful and they waste everyone else’s time in correcting them. If you just want to shoot the bull, there are other forums for that. In General Questions, we prefer that people actually know what they are talking about when they post to a thread.

I bring this up because I have noticed you making similar ill-informed posts in other threads as well, not just this one. You’ll fit in better here if you restrict your comments to subjects you actually know something about.

Colibri
General Questions Moderator